Sorry, to clarify: it isassumed that the first person is heterozygote with black hair as the dominant gene. The question is regarding the first person's recessive gene. Put another way: can one person have a recessive gene that could yield two different offspring, one with red hair and the other with blonde hair?

jcm1757 wrote:Sorry, to clarify: it isassumed that the first person is heterozygote with black hair as the dominant gene. The question is regarding the first person's recessive gene. Put another way: can one person have a recessive gene that could yield two different offspring, one with red hair and the other with blonde hair?

Let's look at this in a much more detailed way. Say, the dominant allele for block hair follicles is B. Since you said that the first person is a heterozygote, the genotype can be written as Bb.

Now, even if the other partner is heterozygotic or double recessive homozygous, there is no chance for BOTH the children not being black. Either one of 'em will always be black... That's dominance of the allele B.

jcm1757 wrote:Sorry, to clarify: it isassumed that the first person is heterozygote with black hair as the dominant gene. The question is regarding the first person's recessive gene. Put another way: can one person have a recessive gene that could yield two different offspring, one with red hair and the other with blonde hair?

Since it's not coded by one gene then yes. Someone here posted great link with an explanation. Try to look it up.